Gastric cancer is the second leading cause of cancer mortality worldwide, accounting for more than 650 000 deaths annually. Since gastric cancers are largely resistant to chemotherapy and radiotherapy, it is of high importance to detect the development of this neoplasm at an early stage. However, early detection of gastric cancer is uncommon.
A detection method presently used is taking x-rays (radiography) of the esophagus, the stomach, and the upper gastrointestinal tract. Administration of a barium solution, and possibly pumping air into the stomach, is carried out to assist in identifying tumors or other abnormal areas. The likelihood of detecting tumors using this method are however believed to be below 50%. A further detection method is endoscopy, an examination of the esophagus and stomach using a thin, lighted fiber optic tube termed “gastroscope”. To confirm accurate diagnosis, the removal of the respective mucosal tissue by endoscopic resection is often required (for most recent data see e.g. Jang, B. K. et al. [2006] Gastrointestinal Endoscopy 63, 5, AB105, S1425), which coincides with cancer treatment. Other screening methods, such as radiographic fluorography or the determination of serum pepsinogen ratios of PGI to PGII, but these are rather experimental and may not detect gastric cancer in the early stages.
There are generally no symptoms in the early stages of gastric cancer, so that the cancer has in many cases spread before it is detected. When symptoms do occur, they are often so vague and nonspecific that patients ignore them. Current laboratory tests for tumor markers are of no value, unless there is already a metastatic liver spread (see e.g. Tierney et al., Current Medical Diagnosis & Treatment 2006, Lange/Mc Graw Hill, pages 596-599). Accordingly, detection of gastric cancer in the early stages or at the stage of intestinal metaplasia may help make routine screening easier facilitating early detection and treatment.
Colonization of the gastric mucosa by Helicobacter pylori, which is considered to confer a high risk for gastric cancer, is known to cause chronic gastritis followed by atrophic gastritis and intestinal metaplasia (INTESTINAL METAPLASIA). While the molecular events associated with Helicobacter infection have been well studied in recent years (Peek, R. M. and Blaser, M. J. (2002) Nat. Rev. Cancer 2, 28-37), the genetic and epigenetic changes required for the initiation of gastric carcinogenesis are still poorly understood, partly because the genes involved in the regulation of growth and differentiation of the stomach epithelium, as well as those involved in carcinogenesis, are not known.
Gastric cancer can be histologically divided into a diffuse type and an intestinal type (Lauren, P. (1965) Acta Pathol. Microbiol. Scand. 64, 31-49). Inactivation of the E-cadherin gene is frequently involved in the diffuse type of familial cancer (Guilford, P. et al. (1998) Nature 392, 402-405) as well as in sporadic cases (Yuasa, Y. (2003) Nat. Rev. Cancer 3, 592-600). Although genetic and epigenetic alterations in the APC, MLH1, TP53, and TGF-β type II receptor genes, and overexpression of the erbB-2 and cyclin E genes have been observed in the intestinal as well as diffuse types (Yuasa, Y. (2003), supra), they only occur in a limited number of cases and have no known roles at the initiation of carcinogenesis.
Recently, a causal relationship between the loss of expression of the Runt-related (RUNX) gene RUNX3 and gastric cancer has been identified (Li, Q. L. et al. (2002) Cell 109, 113-124; International Patent Application WO 02/061069, which is incorporated by reference in its entirety herein). The transcription factor subunit RUNX3, a mouse homolog of the product of the Drosophila segmentation gene runt, is a major nuclear target of the TGF-β signaling pathway (Lund, A. H. and van Lohuizen, M. (2002) Cancer Cell 1, 213-215; Ito, Y. and Miyazono, K. (2003) Curr. Opin. Genet. Dev. 13, 43-47). RUNX3 mediates TGF-β-induced growth inhibition and apoptosis of gastric epithelial cells. The human RUNX3 gene can be inactivated by hemizygous deletion and silencing due to hypermethylation of the promoter region in 40% of stage I and over 90% of stage IV gastric cancers, suggesting that inactivation of RUNX3 takes place in the early stages of carcinogenesis as well as during progression. The tumorigenicity in nude mice of a gastric cancer cell line that failed to express RUNX3 was strongly inhibited by the exogenous expression of RUNX3, but this inhibitory activity was not observed for a RUNX3 allele bearing a rare single amino acid substitution, R122C, which was identified in a gastric cancer patient. Furthermore, cell lines isolated from the gastric epithelium of RUNX3-/- mice were tumorigenic when injected into nude mice whereas those isolated from wild type mice were not. These results suggest that RUNX3 is a tumor suppressor of gastric cancer (Li, Q. L. et al. (2002), supra; International Patent Application WO 02/061069).
With respect to the role of RUNX3 in carcinogenesis, it has been observed that RUNX3 expression is greatly reduced in INTESTINAL METAPLASIA, a tissue frequently observed in association with gastric cancer and characterized by the morphological changes of gastric epithelial cells into cells resembling intestinal epithelial cells (Stemmermann, G. N. (1994) Cancer 74, 556-564). Epidemiologically, INTESTINAL METAPLASIA has been shown to be closely associated with gastric cancer (Sugano, H. et al. (1986) GANN Monogr. Cancer Res. 31, 53-58) and has been discussed as being indicative for the presence of a pre-cancerous state. However, opposing views persist as to the relationship between a pre-cancerous state and INTESTINAL METAPLASIA, and the nature of a relationship, if any, between INTESTINAL METAPLASIA and gastric cancer has not been established.
Accordingly, it is an object of the invention to provide a method that allows for the detection of a cell stage that corresponds to an early onset of gastric carcinogenesis.